1. Field of Invention
The present invention relates to a photosensitive resin composition for a color filter and a color filter formed by the photosensitive resin composition of liquid crystal display (LCD) device thereof. More particularly, the present invention relates a photosensitive resin composition for a color filter having excellent alkali resistance and voltage holding ratio.
2. Description of Related Art
At present, a color filter has been widely used in the application fields of a color liquid crystal display (LCD), a color fax machine, a color video camera and the like. With the increasing market requirements of office equipments such as the color LCD and the like, the methods of producing the color filter tend to diversity, and methods such as a dyeing method, a printing method, an electrodeposition method, a dispersing method and the like have been developed progressively. Now, the dispersing method is the major technique for producing the color filter.
In the aforementioned dispersing method, the pigment is dispersed in the photosensitive resin composition. Then, the photosensitive resin is coated on a glass substrate, followed by the steps of exposure and development, for obtaining a specific pattern. Next, the aforementioned steps of coating, exposure and development are repeated in three times, resulting in the desired red (R), green (G) and blue (B) pixel color patterns in the pixel color layer of the color filter. Typically, for further improving the contrast of the color filter, a light-shielding layer (or called a black matrix) is disposed between the pixel color layers that are formed by pixels.
In the pigment dispersing method, the pigment is firstly dispersed in a photo curing resin to form a coloring photosensitive resin composition. The resin composition finally is formed to a pixel color layer. More specifically, in the pigment dispersing method, a black matrix formed by metals (such as chrome, chromic oxide and the like) or a light-shielding film of the photosensitive resin is disposed on a transparent supporter such as glass substrates and the like. Next, the photosensitive resin (color photo-resist) with the red pigment dispersed therein is spin coated on the transparent supporter. Then, the transparent supporter is exposed by a mask, and developed after the exposure, so as to obtain a red pixel. And then, pixels of three colors red, green and blue can be respectively formed on the supporter by repeating the aforementioned steps of coating, exposure and development.
Recently, the application of the color LCD device is not limited to personal computers but also applied to color televisions and various monitors (especially large-size color LCD screen), such that requirements for color saturation of LCD device becomes stricter. Therefore, a ratio of the pigment in the photosensitive resin composition must be increased. However, when the ratio of the pigment is increased, a contrast of the color LCD device is decreased. Moreover, due to the increased ratio of the pigment, the amounts of an alkali-soluble resin and a photosensitive monomer is decreased relatively, resulting in the reduction of a cross-linking degree of the photosensitive resin composition after exposure, and problems of poor alkali resistance.
In the disclosure of JP Patent publication No. 2004-138950, a specific alkali-soluble resin is formed to a pixel color layer with flat surface and a color filter with excellent pattern configurations, alkali resistance and brightness. However, a voltage holding ratio of the conventionally photosensitive resin composition is bad, thereby easily causing a defect of retained image when an image is displayed.
Thus, there is a need to develop the photosensitive resin composition for the color filter with excellent contrast, alkali resistance and voltage holding ratio for improving the aforementioned defects of the general color filter.